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50-425: See text Xiphophorus is a genus of euryhaline and freshwater fishes in the family Poeciliidae of order Cyprinodontiformes , native to Mexico and northern Central America. Xiphophorus species can be divided into 3 groups based on their evolutionary relationships: platyfish (or platies), northern swordtails, and southern swordtails. Platyfish formerly were classified in another genus, Platypoecilus , which

100-663: A Collector at the College of Agriculture, Cornell University, at McLean Bogs, NY. For two summers after this Gordon was an instructor at Long Island Biological Association, Cold Spring Harbor, Long Island. In 1927, he served as a Biologist with the State of NY Biological Survey (Fisheries) and during the last summers of his Ph.D. he was first an Investigator at Carnegie Institute of Washington, Marine Biological Laboratory, Dry Tortugas, FL. in 1928 and then an Investigator at Marine Biological Laboratory at Woods Hole, Mass. in 1929. Gordon held

150-546: A Ph.D. in zoology, limnology and genetics in 1929. In summers, during school, Gordon worked a variety of jobs. He began in 1920 as a keeper at the New York Zoological Park (now the Bronx Zoo ) and continued from 1921 to 1923 as a Game Keeper, first at the State of Maryland Game Farm, GwynnBrook, MD. and later in 1923 at the State of New York Game Farm, Middle Island, NY. The summer of 1924 saw him work as

200-407: A genus is determined by taxonomists . The standards for genus classification are not strictly codified, so different authorities often produce different classifications for genera. There are some general practices used, however, including the idea that a newly defined genus should fulfill these three criteria to be descriptively useful: Moreover, genera should be composed of phylogenetic units of

250-651: A later homonym of a validly published name is a nomen illegitimum or nom. illeg. ; for a full list refer to the International Code of Nomenclature for algae, fungi, and plants and the work cited above by Hawksworth, 2010. In place of the "valid taxon" in zoology, the nearest equivalent in botany is " correct name " or "current name" which can, again, differ or change with alternative taxonomic treatments or new information that results in previously accepted genera being combined or split. Prokaryote and virus codes of nomenclature also exist which serve as

300-628: A long time and redescribed as new by a range of subsequent workers, or if a range of genera previously considered separate taxa have subsequently been consolidated into one. For example, the World Register of Marine Species presently lists 8 genus-level synonyms for the sperm whale genus Physeter Linnaeus, 1758, and 13 for the bivalve genus Pecten O.F. Müller, 1776. Within the same kingdom, one generic name can apply to one genus only. However, many names have been assigned (usually unintentionally) to two or more different genera. For example,

350-409: A reference for designating currently accepted genus names as opposed to others which may be either reduced to synonymy, or, in the case of prokaryotes, relegated to a status of "names without standing in prokaryotic nomenclature". An available (zoological) or validly published (botanical) name that has been historically applied to a genus but is not regarded as the accepted (current/valid) name for

400-576: A result, inheritance patterns of many traits have been described. More recently, researchers have identified specific genes and even mutations causing pigment pattern variation (for instance, a spot allowing males to mimic females) and investigated selective mechanisms on these traits. Sexual selection : Researchers since Darwin have studied Xiphophorus species for their sexually selected ornaments (e.g. caudal fin "swords"). More recent studies have focused on male ornamentation, courtship strategies, and female mate choice. Genus The composition of

450-427: A taxon; however, the names published in suppressed works are made unavailable via the relevant Opinion dealing with the work in question. In botany, similar concepts exist but with different labels. The botanical equivalent of zoology's "available name" is a validly published name . An invalidly published name is a nomen invalidum or nom. inval. ; a rejected name is a nomen rejiciendum or nom. rej. ;

500-455: A total of c. 520,000 published names (including synonyms) as at end 2019, increasing at some 2,500 published generic names per year. "Official" registers of taxon names at all ranks, including genera, exist for a few groups only such as viruses and prokaryotes, while for others there are compendia with no "official" standing such as Index Fungorum for fungi, Index Nominum Algarum and AlgaeBase for algae, Index Nominum Genericorum and

550-494: A useful model to understand the consequences of hybridization, especially in the context of melanoma research since the 1920s. The Xiphophorus Genetic stock center , founded by Myron Gordon in 1939, is an important source of these fish for research. In addition, several species are commonly kept by aquarium hobbyists, especially the green swordtail ( X. helleri ), southern platyfish ( X. maculatus ), and variable platyfish ( X. variatus ). In fact, these three species comprise one of

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600-587: A variety of professional posts throughout his career; Whilst at the AMNH he developed advanced systems to study genetic and molecular events in melanoma formation. During his tenure at the museum he published a key review The Melonoma Cell as an Incompletely Differentiated Pigment Cell (in M. Gordon (ed.), Pigment Cell Biology, pp. 215–236. New York: Academic Press. 1959). Herbert Axelrod , of TFH Publications , knowing of Gordon's academic reputation and ability to write clearly on any level, recruited him to write

650-713: A very popular series of booklets and magazine features aimed at tropical fish hobbyists. In 1939 he established the Xiphophorus Genetic stock center to provide a reliable supply of genetically identical fish to be used in cancer research. The lines he established remain widely used today. The center was maintained by Gordon and his student Klaus Kallman throughout their tenure at the Aquarium. Kallman transferred it to its current location at Texas State University. Gordon died suddenly in March, 1959 and his obituary in

700-612: Is discouraged by both the International Code of Zoological Nomenclature and the International Code of Nomenclature for algae, fungi, and plants , there are some five thousand such names in use in more than one kingdom. For instance, A list of generic homonyms (with their authorities), including both available (validly published) and selected unavailable names, has been compiled by the Interim Register of Marine and Nonmarine Genera (IRMNG). The type genus forms

750-549: Is not supported by phylogenetic studies, which have shown that the swordtails are paraphyletic compared with the platies. These studies suggest that the genus can be divided into three monophyletic groups: the northern swordtails (of the Pánuco River basin, marked with a star* in the list), southern swordtails (southern Mexico to Honduras) and the platies. The common names given to individual species in this genus do not always reflect their actual relationships; for example,

800-452: Is now obsolete. The type species is X. hellerii, the green swordtail . Like most other new world Poeciliids, platies and swordtails are live-bearers that use internal fertilization and give birth to live young instead of laying eggs like the bulk of the world's fishes. The name Xiphophorus derives from the Greek words ξίφος (dagger) and φόρος (bearer), referring to the gonopodium on

850-460: Is somewhat arbitrary. Although all species within a genus are supposed to be "similar", there are no objective criteria for grouping species into genera. There is much debate among zoologists about whether enormous, species-rich genera should be maintained, as it is extremely difficult to come up with identification keys or even character sets that distinguish all species. Hence, many taxonomists argue in favor of breaking down large genera. For instance,

900-474: Is the type species , and the generic name is permanently associated with the type specimen of its type species. Should the specimen turn out to be assignable to another genus, the generic name linked to it becomes a junior synonym and the remaining taxa in the former genus need to be reassessed. In zoological usage, taxonomic names, including those of genera, are classified as "available" or "unavailable". Available names are those published in accordance with

950-423: Is the origin of spontaneous melanoma in hybrids. For example, in the well-studied Gordon-Kosswig cross between X. maculatus and X. hellerii , hybrids develop spontaneous melanoma due to an interaction between the oncogene xmrk and a repressor locus on a distinct chromosome. Pigmentation: Xiphophorus pigmentation has been investigated since the 1920s using classical genetics techniques such as crosses. As

1000-621: The International Code of Zoological Nomenclature ; the earliest such name for any taxon (for example, a genus) should then be selected as the " valid " (i.e., current or accepted) name for the taxon in question. Consequently, there will be more available names than valid names at any point in time; which names are currently in use depending on the judgement of taxonomists in either combining taxa described under multiple names, or splitting taxa which may bring available names previously treated as synonyms back into use. "Unavailable" names in zoology comprise names that either were not published according to

1050-824: The International Plant Names Index for plants in general, and ferns through angiosperms, respectively, and Nomenclator Zoologicus and the Index to Organism Names for zoological names. Totals for both "all names" and estimates for "accepted names" as held in the Interim Register of Marine and Nonmarine Genera (IRMNG) are broken down further in the publication by Rees et al., 2020 cited above. The accepted names estimates are as follows, broken down by kingdom: The cited ranges of uncertainty arise because IRMNG lists "uncertain" names (not researched therein) in addition to known "accepted" names;

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1100-419: The nomenclature codes , which allow each species a single unique name that, for animals (including protists ), plants (also including algae and fungi ) and prokaryotes ( bacteria and archaea ), is Latin and binomial in form; this contrasts with common or vernacular names , which are non-standardized, can be non-unique, and typically also vary by country and language of usage. Except for viruses ,

1150-404: The platypus belongs to the genus Ornithorhynchus although George Shaw named it Platypus in 1799 (these two names are thus synonyms ) . However, the name Platypus had already been given to a group of ambrosia beetles by Johann Friedrich Wilhelm Herbst in 1793. A name that means two different things is a homonym . Since beetles and platypuses are both members of the kingdom Animalia,

1200-517: The Dec 1959 Copeia noted that "…conclusively demonstrated the heritable nature of melanoma in Xiphophorus and the essential relationship of the macromelanophore to its development…" During his collection trips, he discovered and named several new species, and in 1963, Robert Rush Miller and W. L. Minckley named Xiphophorus gordoni in his honor. The Myron Gordon Award was established to honor

1250-663: The Rio Grande basin (all fully separated), nine restricted species in the Pánuco River basin (mostly separated) and three restricted species in the Coatzacoalcos River basin (mostly separated). The International Union for Conservation of Nature (IUCN) lists the spiketail platyfish ( X. andersi ) and northern platyfish ( X. gordoni ) as Endangered , while the Monterrey platyfish ( X. couchianus ) and marbled swordtail ( X. meyeri ) are listed as Extinct in

1300-617: The aquarium trade: the green swordtail ( X. hellerii ), the southern platyfish ( X. maculatus ) and the variable platyfish ( X. variatus ). These three are the only species that have large native ranges. They have also been introduced outside their native range (in Mexico, Central America, and other continents) where they sometimes become invasive and outcompete and endanger native species, including other, more localized members of Xiphophorus . All other species of Xiphophorus are highly localized and mostly endemic to Mexico. Only three of

1350-442: The base for higher taxonomic ranks, such as the family name Canidae ("Canids") based on Canis . However, this does not typically ascend more than one or two levels: the order to which dogs and wolves belong is Carnivora ("Carnivores"). The numbers of either accepted, or all published genus names is not known precisely; Rees et al., 2020 estimate that approximately 310,000 accepted names (valid taxa) may exist, out of

1400-416: The first appears to be a hybrid between X. variatus and X. xiphidium , and the second between X. variatus and X. couchianus ( X. kosszanderi and X. roseni have not undergone speciation as in X. clemenciae and X. monticolus ). Contemporary hybridization in the wild was thought to be uncommon in this genus until recently. Although traditionally divided into swordtails and platies, this separation

1450-446: The form "author, year" in zoology, and "standard abbreviated author name" in botany. Thus in the examples above, the genus Canis would be cited in full as " Canis Linnaeus, 1758" (zoological usage), while Hibiscus , also first established by Linnaeus but in 1753, is simply " Hibiscus L." (botanical usage). Each genus should have a designated type , although in practice there is a backlog of older names without one. In zoology, this

1500-737: The generic name (or its abbreviated form) still forms the leading portion of the scientific name, for example, Canis lupus lupus for the Eurasian wolf subspecies, or as a botanical example, Hibiscus arnottianus ssp. immaculatus . Also, as visible in the above examples, the Latinised portions of the scientific names of genera and their included species (and infraspecies, where applicable) are, by convention, written in italics . The scientific names of virus species are descriptive, not binomial in form, and may or may not incorporate an indication of their containing genus; for example,

1550-633: The largest component, with 23,236 ± 5,379 accepted genus names, of which 20,845 ± 4,494 are angiosperms (superclass Angiospermae). By comparison, the 2018 annual edition of the Catalogue of Life (estimated >90% complete, for extant species in the main) contains currently 175,363 "accepted" genus names for 1,744,204 living and 59,284 extinct species, also including genus names only (no species) for some groups. The number of species in genera varies considerably among taxonomic groups. For instance, among (non-avian) reptiles , which have about 1180 genera,

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1600-528: The late 1920s. Early papers were published while still a graduate student at Cornell University , but he is best known for his research at New York University and the New York Zoological Society (now Wildlife Conservation Society ). Gordon received his education at Cornell University, achieving first his Bachelor of Science in 1925, going on to study for a Masters of Science in genetics and agriculture, 1925–1926, and finally achieving

1650-412: The lizard genus Anolis has been suggested to be broken down into 8 or so different genera which would bring its ~400 species to smaller, more manageable subsets. Myron Gordon (biologist) Myron Gordon (November 13, 1899 – March 12, 1959) was an American biologist and geneticist and became an expert on platy fish Xiphophorus while using them for his pioneering cancer research, starting in

1700-494: The localized species, the Chiapas swordtail ( X. alvarezi ), X. mayae and X. signum , range outside Mexico and the last two are the only Xiphophorus species not found in Mexico at all. In many locations there are two or more sympatric species, but the localized species are mostly (though not entirely) separated from each other, even when they are restricted to the same river basin. This includes three restricted species in

1750-488: The males. All are relatively small fishes, which reach a maximum length of 3.5–16 cm (1.4–6.3 in) depending on the exact species involved. The various Xiphophorus species range from the southern Rio Grande basin in Mexico, through eastern drainages in the country (river basins draining into the Gulf of Mexico ), to northern Guatemala , Belize and northern Honduras . Three species and their hybrids are common in

1800-526: The marbled swordtail ( X. meyeri ) is actually in the platy group based on its genetics while the short-sword platyfish ( X. continens ) is closer to the swordtails. Swordtails ( Xiphophorus ) Platies ( Platypoecilus ) Hybridization: Xiphophorus is a leading animal model systems in the study of hybridization between species. In particular, studies in Xiphophorus provided some early evidence that recombination controlled patterns of ancestry in hybrid genomes. An interesting consequence of hybridization

1850-641: The memory of an esteemed and respected scientist, Myron Gordon, who is credited with establishing the International Pigment Cell Conferences. The Myron Gordon Award is presented at the International Pigment Cell Conference (IPCC) in recognition of one or more scientists for distinguished and outstanding contributions to the pigment cell field. Established in 1961 after the death of Myron Gordon in 1959 and first presented at IPCC V. Myron Gordon

1900-403: The most (>300) have only 1 species, ~360 have between 2 and 4 species, 260 have 5–10 species, ~200 have 11–50 species, and only 27 genera have more than 50 species. However, some insect genera such as the bee genera Lasioglossum and Andrena have over 1000 species each. The largest flowering plant genus, Astragalus , contains over 3,000 species. Which species are assigned to a genus

1950-505: The most prominent groups of aquarium species, being part of a group of extremely hardy livebearing fish, alongside the molly and guppy , that can adjust to a wide range of conditions within the aquarium. Unlike some species, these are almost always offered as captive bred individuals due to the ease of breeding these livebearers. In captivity, they will coexist with many other fish species, although in an aquarium with too many males and not enough females, fighting can ensue between males of

2000-428: The name could not be used for both. Johann Friedrich Blumenbach published the replacement name Ornithorhynchus in 1800. However, a genus in one kingdom is allowed to bear a scientific name that is in use as a generic name (or the name of a taxon in another rank) in a kingdom that is governed by a different nomenclature code. Names with the same form but applying to different taxa are called "homonyms". Although this

2050-541: The provisions of the ICZN Code, e.g., incorrect original or subsequent spellings, names published only in a thesis, and generic names published after 1930 with no type species indicated. According to "Glossary" section of the zoological Code, suppressed names (per published "Opinions" of the International Commission of Zoological Nomenclature) remain available but cannot be used as the valid name for

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2100-470: The same kind as other (analogous) genera. The term "genus" comes from Latin genus , a noun form cognate with gignere ('to bear; to give birth to'). The Swedish taxonomist Carl Linnaeus popularized its use in his 1753 Species Plantarum , but the French botanist Joseph Pitton de Tournefort (1656–1708) is considered "the founder of the modern concept of genera". The scientific name (or

2150-472: The same species. They can also easily jump out of an inadequately covered aquarium. There are currently 28 recognized species in this genus, according to FishBase . Two of these species, X. clemenciae and X. monticolus , are likely the result of natural hybrid speciation (ancestors of both are a platy species and a swordtail species). Two other proposed species, X. kosszanderi and X. roseni , are recognized by FishBase, but not by all other authorities, as

2200-408: The scientific epithet) of a genus is also called the generic name ; in modern style guides and science, it is always capitalised. It plays a fundamental role in binomial nomenclature , the system of naming organisms , where it is combined with the scientific name of a species : see Botanical name and Specific name (zoology) . The rules for the scientific names of organisms are laid down in

2250-497: The specific name particular to the wolf. A botanical example would be Hibiscus arnottianus , a particular species of the genus Hibiscus native to Hawaii. The specific name is written in lower-case and may be followed by subspecies names in zoology or a variety of infraspecific names in botany . When the generic name is already known from context, it may be shortened to its initial letter, for example, C. lupus in place of Canis lupus . Where species are further subdivided,

2300-412: The standard format for a species name comprises the generic name, indicating the genus to which the species belongs, followed by the specific epithet, which (within that genus) is unique to the species. For example, the gray wolf 's scientific name is Canis lupus , with Canis ( Latin for 'dog') being the generic name shared by the wolf's close relatives and lupus (Latin for 'wolf') being

2350-403: The taxon is termed a synonym ; some authors also include unavailable names in lists of synonyms as well as available names, such as misspellings, names previously published without fulfilling all of the requirements of the relevant nomenclatural code, and rejected or suppressed names. A particular genus name may have zero to many synonyms, the latter case generally if the genus has been known for

2400-576: The values quoted are the mean of "accepted" names alone (all "uncertain" names treated as unaccepted) and "accepted + uncertain" names (all "uncertain" names treated as accepted), with the associated range of uncertainty indicating these two extremes. Within Animalia, the largest phylum is Arthropoda , with 151,697 ± 33,160 accepted genus names, of which 114,387 ± 27,654 are insects (class Insecta). Within Plantae, Tracheophyta (vascular plants) make up

2450-429: The virus species " Salmonid herpesvirus 1 ", " Salmonid herpesvirus 2 " and " Salmonid herpesvirus 3 " are all within the genus Salmonivirus ; however, the genus to which the species with the formal names " Everglades virus " and " Ross River virus " are assigned is Alphavirus . As with scientific names at other ranks, in all groups other than viruses, names of genera may be cited with their authorities, typically in

2500-541: The wild , and thus only survive in captivity. In addition to those, Mexican authorities recognize the yellow swordtail ( X. clemenciae ) and Catemaco platyfish ( Xiphophorus milleri ) as threatened . Almost all the Xiphophorus , including the rare species, have captive populations that are maintained as "insurance" populations at breeding centers and by dedicated private aquarists. Xiphophorus species are regularly used in genetic studies, and scientists have developed many interspecific hybrids ,. Xiphophorus have proved

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